1. Field of the Invention
The present invention relates to a system for measuring approximate figures of, for example, people or cars for indicating a degree of a traffic jam state.
2. Description of the Related Art
There is proposed a system for indicating a state of a traffic jam to control the traffic flow wherein the traffic state is monitored by a TV camera which is set aside the road or wherein the vehicle number or speed of the vehicle is measured from the TV camera by processing the video signal thereof.
Such a system is disclosed, for example, in the Electric Society Report No. 109, 1989, "IV. Municipal Information Service", page 121 to 122, Chapter 1 "2. Traffic Information System".
However, the area which can be covered by one TV camera is limited. Therefore, a plurality of cameras are required to cover the wide area of a traffic state, which makes the system complicated and expensive.
Another traffic monitoring system is such that a traffic counter comprising a supersonic sensor is set on the road to count the numbers of vehicles passing over the sensor. However, in the event of a traffic jam, the detection signal from the sensor is discriminated as if the numbers of vehicles are very small.
The applicant has already filed "System for measuring jam of objects" prior to this application at the Japanese Patent Office, numbered Japanese Laying Open Patent Application No. 3-71300. According to the system of the prior application, the jam degree is measured in such a way that a transmission device is arranged for measuring the objects so that the jam degree is determined from the level of white noise which is transmitted from the transmission device and has a limited band.
However, the sensor of the system is also responsive to the white noise generated from vehicle engines, which impairs the accuracy of the measurement.